Various sizes of paper have become standardized throughout the world for various print jobs. In the United States, business is routinely conducted with “letter” size paper, e.g., 8.5″×11″. In the past, the legal profession used “legal” sized paper, e.g., 8.5″×14″. In Europe, so-called “A4” is used which is a bit narrower and a little longer than “letter” sized paper. Photographs have standardized on 8″×10″, Hagaki, and 4″×6″ print sizes. So a commercial necessity has emerged for printers that can handle all the common sizes of paper now in use.
Large, desktop printers have the luxury of having interchangeable paper trays that can be specialized for each paper size. Some paper trays have adjustable fences that allow different widths of paper to be loaded in a cassette. But small, mobile printers have no slide-in cassette trays at all, and rely on a manual or gravity feed of paper from the top.
Conventional printers can lay a lot of ink on a photo paper printout, and such ink can require a few extras seconds to dry and resist smudging. When more than one photo paper sheet is being printed, the later sheets output can smudge the top ones in the output stack. So it helps if the later sheets are gently dropped flat on the stack.